1. Field of the Invention
The present invention relates to a power amplifier mainly for a high-frequency band, and more particularly to a power amplifier that selectively amplifies a plurality of input signals of different frequencies.
2. Description of the Related Art
There exist radio communication systems for providing services of mobile communication of a plurality of frequency bands. In such systems, radio communication devices, such as mobile terminals, are generally provided with the same number of transmission signal power amplifiers as that of frequency bands used.
For instance, in the personal digital cellular (PDC) system that uses two frequency bands, two power amplifiers for the 800-MHz band and 1900-MHz band are provided in a single mobile terminal. Even a mobile terminal compatible with different systems, such as an 800-MHz-band PDC and 1900-MHZ-band personal handy-phone system (PHS), is provided with power amplifiers dedicated to respective frequency bands.
In a radio communication device, such as a mobile terminal using a plurality of frequency bands, it is difficult to satisfy a demand for size reduction if power amplifiers dedicated to the respective frequency bands.
On the other hand, broadband amplifiers for use in measuring devices can amplify signals of different frequency bands. This type of amplifier, however, consumes much power, therefore is not suitable for mobile terminals that use a battery as a power supply. For this reason, they are not used in mobile terminals.